I don't understand (well, the answer is probably €€€ but I'll make my point anyway) why they don't just have a list of potential stadiums and choose the final venue based on the two teams who qualify for it (size of fanbase, distance, travel convenience etc). Most of these big European stadiums can host a final at the drop of a hat, as the Bernebeu did when they moved the Copa Libertadores there at short notice.